<html>
<head>
  <title>BOOST_PP_VARIADIC_HAS_OPT</title>
  <link rel="stylesheet" type="text/css" href="../styles.css">
</head>
<body>
<div style="margin-left: 0px;"> The <b>BOOST_PP_VARIADIC_HAS_OPT</b> macro
determines whether or not the C++20 __VA_OPT__ construct is supported for the compiler's preprocessor being used. 
Expands to 1 if the __VA_OPT__ construct is supported, otherwise expands to 0.
</div>
<h4>Usage</h4>
<div class="code"> <b>BOOST_PP_VARIADIC_HAS_OPT</b>() <br>
  </div>
<h4>Arguments</h4>
<dl>
  <dt>None<br>
</dt>
</dl>
	<h4>Remarks</h4>
		<div>
			This macro only returns 1 if the compiler is compiling at its own C++20 level and
			__VA_OPT__ is supported. It is possible for a compiler to support the __VA_OPT__
			construct when not compiling at its own C++20 level, but this macro will return
			0 in that case even if __VA_OPT__ is normally supported for that level. The reason
			for this is that such a compiler may have a compiler switch, enforcing a strict
			adherence to a particular C++ standard level, which	gives a warning or an error
			if __VA_OPT__ is specified below the C++20 level, and the preprocessor library
			wants to avoid that happening. Therefore the macro will only test to see whether
			or not __VA_OPT__ is supported at the C++20 level, while otherwise always returning
			0 for all lesser C++ standard levels.
		</div>
<h4>Requirements</h4>
<div> <b>Header:</b> &nbsp;<a href="../headers/variadic/has_opt.html">&lt;boost/preprocessor/variadic/has_opt.hpp&gt;</a>
</div>
<h4>Sample Code</h4>
<div>
<pre>
#include &lt;<a href="../headers/variadic/has_opt.html">boost/preprocessor/variadic/has_opt.hpp</a>&gt;<br>
#if <a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a>()
// Preprocessor code which uses __VA_OPT__
#else
// Preprocessor code which does not use __VA_OPT__
#endif
</pre>
<br>
or within a macro definition<br><br>
<pre>
#include &lt;boost/preprocessor/control/iif.hpp&gt;
#include &lt;<a href="../headers/variadic/has_opt.html">boost/preprocessor/variadic/has_opt.hpp</a>&gt;<br>
#define USE_OPT(...) BOOST_PP_IIF(<a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a>(),MACRO_USING_OPT,MACRO_NOT_USING_OPT)(__VA_ARGS__)
#define MACRO_USING_OPT(...) __VA_OPT__( preprocessor tokens ) anything
#define MACRO_NOT_USING_OPT(...) anything
</pre>
</div>
<hr size="1">
<div style="margin-left: 0px;"> <i></i><i>� Copyright Edward Diener 2019</i> </div>
<div style="margin-left: 0px;">
<p><small>Distributed under the Boost Software License, Version 1.0.
(See accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
</div>
</body>
</html>
